The stack is the piece of software which handles all network connections in a central manner. It's through the TCP/IP stack that all other network applications (including www, instant messaging and email) communicate with the outside world. Most operating systems nowadays have it built in and permanently running in the background, but it's a bolt-on addition to OS3.9 and doesn't run automatically. It's called Genesis, and you can find it in the Internet drawer in your Workbench partition. There's also a preferences program which you use to configure the network. Once you're in there it should be relatively straightforward if you're familiar with networking on other systems...
